An abnormality diagnosis device diagnoses an abnormality of a plurality of speed reducers included in a robot in accordance with disturbance torque regarding a state of the respective speed reducers acquired from a sensor installed in the robot, and outputs a result of the diagnosis to a display unit, the abnormality diagnosis device including a maintenance history DB configured to store maintenance data on maintenance made for the respective speed reducers, and a control unit configured to detect an abnormality in the respective speed reducers in accordance with the disturbance torque. The control unit, when detecting an abnormality in one speed reducer in accordance with the disturbance torque, predicts an abnormality in another speed reducer caused in association with the abnormality in the one speed reducer in accordance with the maintenance data, and outputs information on the predicted abnormality to the display unit.